a) 3x2+12x−66=0

<=> 3(x + 2)2 - 12 - 66 = 0

<=> 3(x + 2)2 - 78 = 0

<=> 3(x + 2)2 = 78

<=> (x + 2)2 = 26

<=> x = √26−226−2

b)9x^2−30x+225=0

<=> (3x - 5)^2 - 25 + 225 = 0

<=> (3x - 5)^2 + 200 = 0

<=> (3x - 5)^2 = -200 (vô lý)
pt vô nghiệm

b) 9x2−30x+225=0

<=> (3x - 5)2 - 25 + 225 = 0

<=> (3x - 5)2 + 200 = 0

<=> (3x - 5)2 = -200

9x2 - 30x + 225 VÔ ngiệm